The Hobbit: Road Back (ressurection, return with the elixir)

Question: Why are last three stages of the archetypal journey in this story significant?

Answer: In 'The Hobbit' the last three stages are significant because it concludes this section of the series and wraps up the book, but in a way it also leaves room for another book to be written. It is also significant because If Bilbo didn't return to the Shire, Frodo would never have gotten the ring, and the next three books wouldn't have been written.
Another reason is because it shows that even though Bilbo was changed by his adventure - he became more daring and more confident in himself - in a way, he was still the same quiet, thoughtful, Shire-loving hobbit he had always been.

"They came to the river that marked the very edge of the borderland of the Wild . . . this was much as it had been before, except that the company was smaller, and more silent; also this time there were no trolls. At each point in the road, Bilbo recalled the happenings and the words of a year ago - it seemed to him more like ten . . . And so they crossed the bridge and passed the mill by the river and came right back to Bilbo's own door . . . There was a great commotion, and people of all sorts . . . He had arrived back in the middle of an auction! . . . In short Bilbo was "Presumed Dead", and not everybody that said so was sorry to find the presumption wrong." (Tolkien The Hobbit 275, 277)